The invention relates generally to optical flame detection.
Flame temperature sensors are needed for control ling a wide range of combustion processes. Some combustion processes that require tight control of fuel-to-air ratios for increased fuel burning efficiency and reductions in emission pollution are present in, for example, building heating systems, jet aircrafts, locomotives, and fossil fueled electric power plants and other environments wherein gas and/or steam turbines are used.
Unnecessarily high combustion temperatures can compromise fuel efficiency and increase emission pollution. For example, in a gas turbine designed to emit nine nitrogen oxide (NOx) particles per million (ppm), an increase from 2730° F. (1499° C.) to 2740° F. (1504° C.) reduces turbine efficiency by about two percent and increases NOx emissions by about two ppm.
Previous silicon carbide flame detectors such as described in Brown et al., U.S. Pat. No. 5,589,682, issued Dec. 31, 1996, detect the presence of a flame and measure the intensity of the flame's photon flux over a wide range of wavelengths. The measured intensity, however, does not always correlate to flame temperature, because intensity is a function of the number of emitting molecules or the amount of fuel being consumed. A ratio of two signals is required to cancel the intensity or fuel factor.
In commonly assigned, Brown, U.S. application Ser. No. 09/561,885, filed May 1, 2000, a continuation-in-part of aforementioned Brown, U.S. Pat. No. 6,239,434, an optical spectrometer for combustion flame temperature determination includes at least two photodetectors positioned for receiving light from a combustion flame and having different overlapping optical bandwidths for producing respective output signals; and a computer for obtaining a difference between a first respective output signal of a first one of the at least two photodetectors with respect to a second respective output signal of a second one of the at least two photodetectors, dividing the difference by one of the first and second respective output signals to obtain a normalized output signal, and using the normalized output signal to determine the combustion flame temperature.
Although the method and system described above provide enhanced flame temperature measurement over conventional methods, disadvantages exist regarding the complexity and cost of multiple photodetector systems. Accordingly, there remains a need in the art of optical flame temperature measurement for a system which provides accurate measurements in a more efficient manner.